C / C++ / MFC

typedef struct tagInputfields
{
    UINT nMask ; 
    CString fields[5] ; 
} ;

CString val = m_ifFields.fields[1] ;

class AA
{
  // private by default.
public:
  AA() { }
};

struct BB
{
  // public by default.
  BB() { }
};

CString tagInputFields::operator[](int idx)
{
  switch ( idx )
  {
    case 1: return field1; break;
    case 2: return field2; break;
    // and so on...
    default: /* some kind of error handling here */
      return _T("");  // fall back case, empty string
  }
}
 
const CString tagInputFields::operator[](int idx) const
{
  switch ( idx )
  {
    case 1: return field1; break;
    case 2: return field2; break;
    // and so on...
    default: /* some kind of error handling here */
      return _T("");  // fall back case, empty string
  }
}

// this is in a header file shared by the EXE and the DLL projects
class MyCallBacks
{
 virtual void Callback1(parameters) = 0;
 virtual bool Callback2(parameters) = 0;
}

// this is in your EXE
CMyDialog : public CDialog, public MyCallbacks
{
 // implementations of the callback functions
 void Callback1(parameters);
 bool Callback2(parameters);
}

// this is in your DLL
if (m_pCallback != NULL)
{
m_pCallback->Callback1(parameters);
}